1. Field of the Invention
The present invention relates to printers adapted for a sheet transfer control, and in particular to a printer adapted for a sheet transfer control with a sheet circulating transfer route including a sheet invert portion for inverting a sheet between front side and back side.
2. Description of Related Art
There has been known printers configured with a sheet circulating transfer route including a sheet transfer portion of a printing mechanism and a sheet invert portion. The printers are adapted for a sheet with a print made on one side thereof by the printing mechanism to be inverted at the sheet invert portion, to make a print on the opposite side by the same printing mechanism. A recent trend of demands for printers with increased printing speeds is directed to implement a high productivity of print material by a high speed printing not only simply in one-side printing but also in both-side printing.
The productivity of print material mainly depends on a transfer speed of sheet commensurate with a printing speed at a sheet transfer portion of a printing mechanism. The transfer speed has been ruling transfer speeds of sheets at other sections of a sheet circulating transfer route in the past. Japanese Patent Application Laid-open Publication No. 2005-280897 discloses a printing technique that both-side printing of sheets is alternately done to a front side of a sheet and a back side of another sheet and transfer speeds in a sheet circulating transfer route are controlled in accordance with an associated sheet size, independently from a transfer speed at a printing mechanism. This technique permits a sufficient inter-sheet spacing to be secured with an enhanced productivity of print material.